First, several types of conventional light transmitting material will be reviewed, which are used for the light emission at the end of these materials.
In regard to light transmitting materials capable of being used, e.g. for light signal transmission such as for in-vehicle wiring, mobile wiring and FA device wiring, optical sensors such as liquid surface level sensors or pressure sensors, image guides such as fir endoscopes, light guides such as for decorative displays, home electric appliances, optical devices, outdoor signages, etc., there have been provided several materials as below.
There has been a material, of which core material and clad material are both composed of inorganic glass material such as silica glass or multicomponent glass.
There has also been a material, of which core material and clad material are both composed of PMMA (polymethyl methacrylate) plastic material.
There has also been a material, wherein a tubular clad material having small refractive index, such as silicone polymer or fluorocarbon polymer, is used, and a plastic material such as organo-polysiloxane having higher refractive index than that of the tubular clad material and serving as a core material, is filled and hardened in that tubular clad material.
There has also been a material, wherein a tubular clad material having small refractive index, such as silicone polymer or fluorocarbon polymer, is used, and a liquid or fluid transparent material having higher refractive index than that of the tubular clad material and serving as a core material, is filled and sealed in that tubular clad material (See Japanese Unexamined Patent Publication No. Hei 11-190808).
Further, there has also been a material, of which clad material is composed of fluorocarbon polymer, etc., and of which core material is composed of polycarbonate resin or norbornene resin, etc., having higher refractive index than that of the clad material (See Japanese Unexamined Patent Publication No. 2000-275448).
However, the conventional light transmitting materials discussed as above have the allowing problems.
First, in the case of a light transmitting material of which core material and clad material are both composed of inorganic glass material, when this type of light transmitting material is used e.g. as a light guide, this material would express the good light transmitting property, having almost no decrease of light volume for a wide frequency. However, because a bundle of a large number of very thin light transmitting materials (each of which outer diameter is about 10 μm) is used as a single light transmitting material, it would require the bundling process, as well as bundling components such as bundling tubes or bundling metal fittings, which would result in higher production cost.
Second, the reference is made to a light transmitting material of which core material and clad material are both composed of PMMA, plastic material. In the case of this light transmitting material, the transmission loss value is good (about 0.2 dB/m). However, the wiring workability is poor due to insufficient flexibility, and when being bent and used, the material would present a considerable adverse effect of decrease of light volume and increase of transmission loss value, and accordingly, the using purpose of this material is considerably limited. Further, this light transmitting material is very hard, and when the end faces are merely cut, the material would present a considerable adverse effect of decrease of light volume and increase of transmission loss value, and accordingly it is necessary to polish the both end faces, which would result in higher production cost.
Third, the reference is made to a light transmitting material wherein a plastic material such as organo-polysiloxane, serving as a core material, is filled and hardened in a tubular clad material. This light transmitting material has the transmission loss value at about 1.0 dB/m and in normal state, this type of material has the good light transmission property with almost no adverse effect of decrease of light volume or increase of transmission loss value. However, the material would become clouded under high temperature and high humidity or in the warm water, and would present a considerable adverse effect of decrease of light volume and increase of transmission loss value. To cope with these problems, for example with reference to Japanese Patent No. 3024475, it has been suggested that, modified polyorgano siloxane, causing no adverse effect of decrease of light volume or increase of transmission loss value, under high temperature and high humidity or in the warm water, is used as a core material. However, the modified polyorgano siloxane is a special and very expensive material, the cost of light transmitting material would become considerably high.
Fourth, in the case of a light transmitting material wherein a liquid or fluid transparent material serving as a core material is filled and sealed in a tubular clad material, it is necessary to apply laborious end sealing process to the both ends of material, such as sealing by sealer and adhering to the clad material, or covering the clad material by metal sleeve so that the both ends of the sleeve may be tightly fastened, and consequently, the production cost would become higher. In addition, since the sealing of the both ends is required, when the material is actually used, it is impossible to cut the material at a desired length, which would result in a very limited using purpose.
Further, in the case of a light transmitting material, of which clad material is composed of fluorocarbon polymer, etc., and of which core material is composed of polycarbonate resin or norbornene resin, etc., the transmission loss value is about 1.0 dB/m. However, for the purpose of preventing from becoming clouded under high temperature and high humidity or in the warm water, as suggested in Japanese Unexamined Patent Publication No. 2000-275448, it is necessary to be provided with a double-layer structure of clad material, which would result in a higher production cost. In addition, when the material is exposed in high temperature in a moment, there would be the deformation of light transmitting material due to shrinkage or fusion thereof, which would result in a serious fault of being incapable of carrying out the function as a light transmitting material. Consequently, this material cannot be used for wiring at the places expected to become abnormal temperature.
Now, several types of conventional light transmitting material will also be reviewed, which are used for the light emission from the side of these materials.
For example, neon tubes or fluorescent tubes are used as a light source or decorative displays, home electric appliances, outdoor signages and various illumination devices. However, these devices would require high voltage, and therefore, if they are used in the water or in any water-affected place such as being exposed in the rain, there would be a risk of electric shock or electric leakage. In addition, since these tubes are made of glass and may be broken easily, which would also result in a very limited using purpose.
Therefore, recently, as the alternative material, there have been provided a various type of side-emitting optical fibers, wherein, the light is incident in at least any one end of the optical fiber, comprising a core and a clad, in the longitudinal direction, and the light is emitted in the circumferential direction (from the side face) of the core and the clad.
For example, with reference to Japanese Unexamined Patent Publication No. 2000-131529, there is provided a light transmitting tube, comprising a transparent core material, and a clad material having smaller refractive index than that of the core material, wherein scattering particles, e.g. organic polymer particles such as silicone resin particles or polystyrene resin particles metal oxide particles such as Al2O3, TiO2, SiO2, sulfate particles such as BaSO4, and carbonate particles such as CaCO3, is dispersed in the core material. According to this light transmitting tube, in regard to the core material, there has been disclosed (meth)—acrylic polymer such as methylmethacrylate (MMA), and in regard to the clad material, there has been disclosed fluorocarbon polymer such as tetrafluoroethylene-hexafluoropropylene copolymer (FEP), as preferable materials.
With reference to Japanese Unexamined Patent Publication No. 2000-321444, there is provided an optical fiber, comprising a core material made of resin, and a clad material made of resin and having smaller refractive index than that of the core material, wherein the core material is mixed with particles, of which refractive index is different from that of the core material, and of which specific gravity is between 70% and 130% of that of the core material. According to this optical fiber, in regard to the core material, there has been disclosed silicone rubber, in regard to the clad material, there has been disclosed fluorocarbon resin such as tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and in regard to the particles, there has been disclosed microcapsules which will be expanded when the heat is applied thereto, as preferable materials.
However, the conventional light transmitting materials discussed as above have the following problems.
First, in the case of light transmitting tube disclosed as Japanese Unexamined Patent Publication No. 2000-131529, the wiring workability is poor due to insufficient flexibility, and when as the diameter becomes lager, it would become more difficult to place in an arbitrary form, and accordingly, the using purpose of this material is considerably limited. Further, this light transmitting tube is very hard, and when the end faces are merely cut, the material would present a considerable decrease of side face light emission volume due to the serious loss of light introduction, and accordingly it is necessary to polish at least the light incident end face, which would result in higher production cost.
Second, in the case of optical fiber disclosed as Japanese Unexamined Patent Publication No. 2000-321444, this optical fiber has a good flexibility and it is possible to place in an arbitrary form even if the diameter becomes larger. Further, in normal state, this optical fiber has a good side face light emission property, because there is almost no decrease of side face light emission volume. However, when used under high temperature and high humidity or in the warm water, the material would become clouded, which would result in considerable decrease of the side face light emission volume. To cope with this problem, for example with reference to Japanese Patent No. 3024475, it has been suggested that, modified polyorgano siloxane, causing no adverse effect of decrease of side face light emission volume, under high temperature and high humidity or in the warm water, is used as a core material. However, the modified polyorgano siloxane is a special and very expensive material, the cost of light transmitting material would become considerably high.
Now, several types of conventional structure between light transmitting material and optical device will be reviewed.
When light transmitting material is used, the technology to connect the light transmitting material with optical device is required for the purpose of improving the convenience, and various technologies have been investigated. In regard to light transmitting material and optical device, there have been investigated those comprising PMMA plastic material, or those comprising silicone polymer, etc.
For the purpose of connecting these light transmitting material with optical device there has been investigated the following methods. When connecting a light transmitting material with an optical device, both comprising PMMA plastic material, it has been investigated that, the end face of the light transmitting material is in contact with the end face of the optical device, or the each end face has been armed to be a substantially half-round section face or a predetermined length, and is in contact with each other, and thereafter, the contact face is connected by adhesive or ultrasonic welding machine. Further, reference is made to a method for connecting, in the case that one of the light transmitting material and the optical device is made of PMMA plastic material, and that the other is made of silicone polymer. In this method, it is possible to connect liquid silicone polymer before the hardening reaction with the optical device made of PMMA plastic material, in which the silicone polymer may serve as adhesive by hardening reaction itself. When connecting a light transmitting material with an optical device, both comprising silicone polymer, any of the above method may be used.
When connecting a light transmitting material with an optical device, both comprising PMMA plastic material, it is understood that, in regard to the structure of connecting part, the contact face between the core material of the light transmitting material and the core material of the optical device is not covered by the clad material of the light transmitting material. On the other hand, when connecting a light transmitting material with an optical device, any of which is made of PMMA plastic and the other of which is made of silicone polymer, or when connecting a light transmitting material with an optical device, both of which are made of silicone polymer, it is understood that, in regard to the structure of connecting part, the contact face between the core material of the light transmitting material and the core material of the optical device is covered by the clad material of the light transmitting material.
However, the conventional connecting structure discussed as above have the following problems. With reference to a combination of light transmitting material with material of optical device, firstly, when PMMA plastic material is used for both the light transmitting material and the optical device, the contact face between the core material of the light transmitting material and the core material of the optical device is not covered by the clad material of the light transmitting material, in other words, the core material and the clad material are positioned on the same plane at the contact face. Consequently, with reference to the contact face on which the scatter of light would easily occur, when the scatter of light occurs at the contact face of the core material, the scattering light at the contact face of the core material would easily go out of the contact face of the clad material, and further, the scatter of light would further occur easily at the clad material, which would enhance decrease of light volume and increase of transmission loss value.
When the contact face between the light transmitting material and the optical device is not covered by the clad material of the light transmitting material, as compared with the case in which the contact face of the clad material is not positioned on the same plane as the contact face of the core material, the contact area would become smaller, thus it is difficult to obtain the sufficient connecting strength. Further, if the sufficient flexibility is not provided for any of the light transmitting material or the optical device, or for both of them, when any force such as warping is applied thereto, it will be impossible to absorb such a warping force, etc. by any flexible part, which might cause the destruction of contact face. Consequently, it will be difficult to simply obtain practically sufficient connecting strength, and the destruction might occur easily, which would pose the problem of difficulty for practical application.
Further, in the case that one of the light transmitting material and the optical device is made of, or the both of them are made of silicone polymer, when one of them has become in contact with the other before the hardening reaction of silicone polymer, they will be connected with each other, because of the silicone polymer serving as adhesive by hardening reaction itself. This connecting structure has flexibility, thus it is possible to obtain practically sufficient connecting strength. However, when silicone polymer is used, there would be the problem of becoming clouded under high temperature and high humidity or in the warm water, which would cause the adverse effect of decrease of light volume or increase of transmission loss value, and it will be impossible to carry out the function as light transmitting material or optical device.
In the light of the above problems, it is an object of the present invention to provide a light transmitting material characterized by having almost no adverse effect of decrease of light volume or increase of transmission loss value when being bent, having almost no adverse effect of decrease of light volume or increase of transmission loss value under high temperature and high humidity or in the warm water, being free from deformation when exposed in high temperature in a moment, and being capable of stably maintaining an excellent light transmitting property for a long period of time, having sufficient flexibility even if the diameter is increased. It is also an object of the present invention to provide a method for manufacturing such a light transmitting material at a lower production cost.
Further, it is another object of the present invention to provide a light transmitting material (light scattering material), characterized by easy and arbitrary forming to be placed at any position because of the soft and flexible property even if the diameter is increased, having no risk of being damaged because of the good impact resistance, having almost no adverse effect of decrease of side face light emission volume under high temperature and high humidity or in the warm water, and being capable of stably maintaining an excellent side face light emission property for a long period of time. It is also another object of the present invention to provide a method for manufacturing such a light transmitting material (light scattering material) at a lower production cost.
Further, it is also another object of the present invention to provide a structure connecting light transmitting material and optical device, characterized by having small adverse effect of decrease of light volume or increase of transmission loss value at the connecting part, having practically sufficient connecting strength, and having almost no adverse effect of decrease of light volume or increase of transmission loss value under high temperature and high humidity or in the warm water.